Patent Grant
9165493
This application is related to, and incorporates by reference, U.S. patent application Ser. No. 12/251,186, filed Oct. 14, 2008 and entitled “Color Correction of Electronic Displays.”
The present invention generally relates to display correction and, more specifically, to correcting the displayed color by reducing its dependency on various variables, such as temperature.
Many computing devices use an electronic display to present information to a user. Such displays may be, for example, liquid crystal displays (“LCDs”), cathode ray tubes (“CRTs”), organic light emitting diode displays (“OLED displays”) and so on. Most such displays can show color images. However, the color response of a display may change as the display operates.
In particular, the display's white point may shift along a blackbody curve as the physical temperature of the display reaches a steady operating temperature. For example, when a display is turned on, the display may be cold and the temperature of the display may increase as the display warms up over time. The changing temperature of the display may cause the display colors to shift. For example, some displays depict white as somewhat yellowish when initially powered on and cold. As the display warms, the white point of the display shifts toward a more neutral white, such as defined by the standard illuminant, D65. The same is true for any colors shown on the display; they too shift within a color space as the temperature of the display increases. This is true even if, for example, the display only outputs grayscale colors (e.g., is a black and white display). Similarly, other parameters of the display may shift as a function of temperature such as luminance, black level, contrast, or electro-optical transfer function, which may be referred to as the “native gamma” of the display. This set of parameters may be referred to as the color profile of the display.
The shift in the color profile due to temperature increase of the display generally causes each pixel of the display to change color until a stable operating temperature is achieved, at which point the pixel colors are likewise stable. That is, although a pixel may be instructed to display the same color at an initial temperature and a stable operating temperature, the actual color displayed, as objectively measured by its chrominance and luminance, may vary. It should be noted that, in many electronic systems, individual pixels of a display receive a red, green and blue value that together define the color to be created by the pixel. These red, green and blue values are referred to herein in the aggregate as an “RGB value,” as understood to those of ordinary skill in the art.
Thus, a method of adjusting the display colors over a range of display temperatures is desirable. Accordingly, there is a need in the art for an improved method of providing consistent display colors over a range of parameters including temperature.
In an embodiment, a display device receives video input and utilizes a video-rendering chip to perform gain correction on the video input, based on a display temperature, to produce output values. The output values are provided to a display driver which controls the hardware of the display to show the output values on the display.
The video-rendering chip includes a videorendering engine, a microprocessor, and a memory. The microprocessor receives a sampled display temperature from a temperature sensor, determines correction coefficients that correspond to the sampled display temperature, and provides the correction coefficients to the video-rendering engine. The video-rendering engine then utilizes multipliers to multiply the display input by the correction coefficients to produce the output values. The video-rendering engine may utilize a dithering component to dither the output values before providing the output values to the display driver.
In some embodiments, the microprocessor may determine the correction coefficients by retrieving the correction coefficients that correspond to the sampled display temperature from a lookup table stored in the memory. The lookup table stored in the memory may include correction coefficients that correspond to the sampled display temperature. Alternatively, the correction coefficients may be interpolated from correction coefficients that correspond to other display temperatures included in the lookup table. In other embodiments, the microprocessor may determine the correction coefficients by retrieving a correction coefficient formula stored in the memory and applying the correction coefficient formula to the sampled display temperature to produce the correction coefficients.
The microprocessor may receive a sampled display temperature periodically. After the microprocessor receives the display temperature at a first time and determines correction coefficients that corresponded to the sampled display temperature at the first time, the video-rendering engine may apply the correction coefficients that corresponded to the sampled display temperature at the first time to received display input until the microprocessor received a sampled display temperature at a second time. After the microprocessor received the display temperature sampled at the second time, the microprocessor determines correction coefficients that correspond to the display temperature sampled at the second time and the video-rendering engine applies the correction coefficients that correspond to the display temperature sampled at the second time to the display input received after the second time.
In some embodiments, the video-rendering chip may sample the display temperature at fixed periods, such as every second. In other embodiments, the video-rendering chip may vary the periods at which the microprocessor receives the sampled display temperature based on the previously sampled display temperature.
Generally, one embodiment of the present invention may take the form of a method for adjusting the color of a display to account for the color shifts due to operating temperature changes. In this embodiment, a display temperature may be used as an input to determine an adjustment value. The adjustment value may be found in a look-up table or may be computed by interpolating from the values found in the table. Continuing the description of this embodiment, the adjustment value may be applied, depending on the type of display, to an RGB value that may be supplied to each pixel or to the gain of the red channel, green channel and blue channel to adjust the color of the display.
Another embodiment may take the form of a method for correcting display colors as a display warms up and changes temperature. In this embodiment, data such as luminance and chrominance values may be recorded for different RGB input values to the display, for every temperature in a set of temperatures. The recorded data may be stored in memory or as a data file. The display may produce a color range that may be referred to herein as the “display color gamut.” The display color gamut may then be constructed based on the recorded data using either a matrix multiplication and gamma correction based model (called the matrix model) or a look-up table and optional interpolation based model, called the “LUT model.” Generally, a color model is a way of representing the correspondence between colors as measured by an instrument on the display and the RGB numbers that produces these colors on the display. The table based model may be created, for example, by empirically measuring luminance and chrominance for a variety of pixel colors expressed in RGB values and comparing them to desired or perceived luminance and chrominance values.
These desired values generally correspond to the luminance and chrominance that are set as the luminance and chrominance target values for that display. The target may correspond to the luminance and chrominance of the displayed color when the electronic display has achieved its stable operating temperature. Alternatively, the target may correspond to a different set of luminance and chrominance values. For example, the target may be those recommended by a certain standard or selected by the user according to particular needs. As another example, a fixed luminance and D65 reference white point may be used as a target. Also, the target may be specified by a luminance and white point value that varies according to a precise function selected by the user. In short the target as luminance and white point can be an arbitrary set. At various temperature values, certain color models may be more suitable than others for coding the colors produced by that device. There may be multiple color models such that each individual color model corresponds to a specific temperature. Thus, as the temperature of the display increases, the color model of the display (or its component pixels) may change.
A target state of the display may be defined as a white point value and a luminance value of the display. For a specific temperature for which the parameters of the color model have been measured, the adjustment values for each R, G and B components may be computed using the color models and the target luminance and white point value. The RGB adjustment values may be organized into an table such that each line in the table provides the RGB adjustment values corresponding to specific temperature. For an arbitrary temperature value that is not included in the table, the corresponding RGB adjustment values may be computed by interpolating the RGB adjustment values in the table. As used herein, this table will be called RGB table.
It should be noted that embodiments of the present invention may be used in a variety of optical systems and image processing systems. The embodiment may include or work with a variety of display components, monitors, screens, images, sensors and electrical devices. Aspects of the present invention may be used with practically any apparatus related to optical and electrical devices, display systems, presentation systems or any apparatus that may contain any type of display system. Accordingly, embodiments of the present invention may be employed in computing systems and devices used in visual presentations and peripherals and so on.
Before explaining the disclosed embodiments in detail, it should be understood that the invention is not limited in its application to the details of the particular arrangements shown, because the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.
Also as depicted in
The chromaticity diagram of
Generally, a display may produce a color depending on the RGB input signal. Ideally, when the RGB input signal is fixed, the displayed color should also be fixed. However due to the variation of the temperature of the display from cold to warmed up, some internal parameters of the display may change, affecting the luminance and the chromaticity of the displayed color, even if the RGB input signal was not changed. This may occur because the displayed color may vary with the temperature.
A display includes multiple pixels arranged in a matrix of rows and columns. Each pixel may generate a color corresponding to an RGB value communicated to the pixel, typically by an application or operating system executed by an associated computing device. For example, each pixel may include multiple subpixels; a single subpixel may correspond to one of a red, green and blue channel. The operation of pixels and constituent subpixels to create color is known to those of ordinary skill in the art.
In one example and as depicted in
Continuing the discussion of this embodiment, the display 300 may include a temperature sensor 310. The temperature sensor 310 may measure a display temperature and provide it to the firmware 320. Generally, the firmware 320 may be embedded in the display 300 and executed by a device such as a microcontroller or a microprocessor (not shown). The firmware 320 may request an adjustment value from an RGB table 335 for the temperature provided by the temperature sensor 310. The firmware 320 may then receive the adjustment value from the RGB table 335. The adjustment value may be based at least on the display temperature provided by the temperature sensor 310 and may be used to adjust the color on the display 300. The RGB table 335 may be stored in a memory which may be a memory such as an electrically erasable programmable read-only memory.
The firmware 320 may apply the adjustment value to either the input RGB values or to the gain control of the RGB channels. The adjustment value may change the display colors such that the display colors may appear as the target color. The adjustment values of the RGB table 335 may be applied to the input RGB values to the display and/or the gain of the RGB channels of a display. By applying the adjustment values to the input RGB values, the RGB values transmitted to the display may be changed. However, applying the adjustment values to the gain of the RGB channels may change the displayed color without altering the RGB values transmitted to the display. Accordingly, by applying the adjustment values to either the input RGB or to the gain of each RGB channels, the displayed colors may approximate the desired output and thus remain relatively constant as the display warms up and changes temperature. The adjustment values may be attenuation factors. The adjustment values and the RGB table 335 will be discussed in further detail below. Adjusting the displayed color by applying the adjustment value from the RGB table 335 will also be discussed in further detail below.
In one example, at a certain display temperature, a displayed color corresponding to an input RGB value may not correspond to the target color. In this example, an adjustment value corresponding to the display temperature may be determined from the RGB table 335. The adjustment value may be three values, an adjustment value for the red channel, an adjustment value for the green channel and an adjustment value for the blue channel. For explanatory purposes, although the adjustment value may be three values, it may be referred to herein as “the adjustment values.” Additionally, the terms “RGB channel gain” and “input RGB values” may be referred to herein as “RGB values”. Still continuing this example, the adjustment value may be applied to the RGB values so that the displayed color appears as the target color even though the display may be at a temperature different from the stable operating temperature.
Each set of adjustment values may be stored in the RGB table 335. Typically, each such set of adjustment values corresponds to a single temperature and is indexed in the RGB table 335 by the corresponding temperature. By constructing the RGB 335 table in this manner, the firmware may relatively easily retrieve the set of adjustment values necessary to modify the input RGB values for a given pixel in order to produce the desired output, so long as the current operating temperature of the display 300 is known by the firmware.
In
where RGB1 through RGBm are the RGB values that may produce a white corresponding to the target white at the temperature T1 through Tm respectively, when applied to the RGB value of the display. The RGB1 through RGBm values may be used to compute the adjustment values R1 through Rm for the red component, G1 through Gm for the green component and B1 through Bm for the blue component for the temperature T1 through Tm respectively.
The adjustment values may be determined for each RGB channel at a specific temperature. The adjustment value for an arbitrary temperature T, may be computed by using the ratio:
Rx=Rt/Rw
Gx=Gt/Gw
Bx=Bt/Bw
where Rx, Gx, Bx may be the RGB values interpolated from two RGB sets from the RGB table corresponding to the temperatures T1, T2 that defines the smallest temperature interval containing the temperature T. Additionally, Rw, Gw, Bw may be the RGB values corresponding to the color white at the stable operating display temperature. Rx, Gx, Bx may be the adjustment value for each RGB channel at the arbitrary temperature, T. Once the adjustment values are determined, they may be used in firmware and/or software.
By applying adjustment values to the RGB values for a display, the luminance and chrominance values are effectively stabilized for the temperature range of the display. By applying the adjustment values, the measured luminance and chrominance values may be equivalent to the target luminance and chrominance values. The target luminance and chrominance values may be the luminance and chrominance values after the display has warmed up and reached a stable temperature. Before applying the adjustment values to the RGB values in the display, the output luminance and chrominance values may shift with temperature as shown in
Additionally, adjustment values may also be determined for any value of input parameter and/or combination of input parameters, including those not originally recorded, by employing an interpolation method. The input parameters and adjustment values may be organized into an RGB table as shown above. The adjustment values may compensate for the shifting luminance and white point values over the change in display temperature as the display warms up. The adjustment values may be used to adjust the color of a display to appear as it would after the display has sufficiently warmed up to a stable temperature. The method of constructing the color model may not change the resulting RGB table, however the table size may vary corresponding to combinations of the input parameters. (As discussed herein, the color model may be constructed in a number of ways including, but not limited to, using the look-up table based model or the matrix model.) The implementation of the RGB table in firmware was previously discussed with respect to
The RGB table discussed above may be derived from sets of color gamuts. A color gamut may be constructed in a number of ways. The color gamut may represent the range of possible colors that a monitor may display for a given temperature.
In one embodiment, the color gamut may be constructed by employing a look-up table based model and the color gamut may be an empirical model. In this embodiment a set of RGB values may be predetermined. The selection of the set of predetermined RGB values may be based on the number of desired values for each color. For example, six values between 0 and 255 may be chosen for the red component, six values between 0 and 255 may be chosen for the green component and six values between 0 and 255 may be chosen for the blue component. For every combination of the six values for each of the three components, a luminance (Y) and a chrominance (x, y) may be measured. These measurements may be repeated for a number of different temperatures.
As shown in
Returning to constructing a color gamut, a predetermined set of RGB values may be defined. In this example, at each operating temperature T1 through Tm, the luminance (Y) and the chrominance (x, y) may be measured for each of the RGB values in the predetermined set of RGB values. If the matrix color model is used, four color measurements for pure red, pure green, pure blue and pure white, at each temperature T1, through Tm, may be used for the display. For example, pure red may be 255, 0, 0, pure green may be 0, 255, 0, pure blue may be 0, 0, 255 and pure white may be 255, 255, 255.
If a look-up table model is used with 216 samples (6×6×6=216), the measurements may be taken of luminance (Y) and chrominance (x, y) for 216 predetermined RGB values. The 216 RGB values may result from selecting six values for each of the individual RGB values and providing all possible combinations of the six values for each RGB value. The 216 RGB values is provided for explanatory purposes only. For example, at a temperature T1, a luminance and chrominance measurement may be taken for each of the 216 predetermined RGB values. Similarly, for a temperature T2, another luminance and chrominance measurement may be taken for each of the 216 predetermined RGB values and so on. Additionally, the number of samples per each component may be increased (for example, using seven or more values for each of the individual RGB values), thus increasing the accuracy of the empirical model.
Each color gamut CG1 through Cgm may be defined at each temperature T1 through Tm respectively, thus the RGB table may be calculated once the target luminance and white point values are set. The calculation of the RGB table may be performed line by line. Each line in the table may correspond to a temperature T1 through Tm, thus RGB table may have m lines. For each line, k, in the RGB table, the RGB values may be computed as follows. For temperature Tk, the target luminance and white point values may correspond to a unique color in the color gamut Cgk. The unique color may be produced by a certain RGB value, RGBk. Resolving the RGBk color for a given target color and color gamut may depend on the color model that is used for the display. For example, if the matrix model is used, the following equations are used to compute RGB from Yxy of the target:
X=x·Y/y, Z=(1−x−y)·Y/y
[rlinear glinear blinear]t=M−1·[XYZ]t
R=rTRC−1[rlinear]
G=gTRC−1[glinear]
B=bTRC−1[blinear]
where
If the look-up table model is used, the calculation of the RGB with a defined color gamut as a table of (RGB Yxy) sets, may be based on tetrahedral decomposition and tetrahedral interpolation, which are known to one of ordinary skill in the art.
Each predetermined RGB value may include a value for the red channel, green channel and blue channel of a display pixel. Thus, each RGB value may be expressed as a set of three numbers controlling the intensity of the red, green and blue components. For example, the three numbers may range from zero to 255. A zero value means no color is emitted by the corresponding channel while a 255 value means the channel emits light at full intensity. Thus, a RGB value of (255, 0, 0) may correspond to the red channel operating at full power while the green and blue channels are off. Likewise, a RGB value of (255, 255, 0) may instruct a pixel to create yellow color by combining full-intensity red and green light from the respective component but leaving the blue component entirely off. It should be appreciated that these are examples of 24-bit color; each color channel has eight bits dedicated to it. Alternative embodiments may employ greater or fewer bits per color channel.
Returning to the discussion of
where the measurements (Yxy)1 through (Yxy)n correspond to the temperature T1. Accordingly, multiple luminance and chrominance values (Y and (x,y), respectively) may be measured for a variety of predetermined RGB values R1, G1, B1 to Rn, Gn, Bn at a single operating temperature T1. Also, n is the number of luminance and chrominance measurements taken at each operating temperature. For every selected operating temperature T1 through Tm, color gamuts CG1 through CGm may be constructed for each corresponding temperature. The construction of the color gamuts may be based on the color model that employ the measurements at each temperature T1 through Tm. The measurements taken at each of the temperatures T1 through Tm may be selected to cover the range from approximately the cold start-up temperature of the display to the stable operating temperature of the display. In one example, the last or stable operating temperature may be the display temperature after the display has been on for approximately two and a half hours. Generally, the color table for the last temperature may be represented as:
Thus, m color gamuts CG1 through CGm may be constructed using the temperatures, predetermined RGB values, luminance measurements and chrominance measurements and the color model at each temperature T1 through Tm. The m color models may be represented as:
In another embodiment, a color model may be constructed using a matrix model. The matrix model may employ the measurements of the following colors: the display red, green, blue and white colors, and a set of intermediates gray colors between black and white for tone reproduction curve estimation. For this embodiment, 6 intermediate gray colors may be used. The luminance measurements Y and the chrominance measurements (x,y) may be taken for a predetermined set of RGB values specified by the following n=4+6 combinations, and the (Yxy)j,k may represent the measurements for the color model k at temperature Tk, k=1 through m and for the combination j, where j may be a natural number from 1 through n=10.
The tone reproduction curve in the matrix model may be determined at each temperature T1 through Tm from the measurements Y5,k through Y10,k using an interpolation method familiar to one of ordinary skill in the art. In this embodiment, linear interpolation was employed.
In another embodiment, a color model may be constructed using a matrix model where the tone reproduction curves may be independent of the temperature and estimated before the color measurements are taken at the temperature T1 through Tm. The measurement of the intermediate gray colors may be done at the initial cold or warmed up stable display temperature. The curves may be derived through interpolation one time and may be used for each color model at temperature T1 through Tm. For this embodiment, the matrix model may employ the measurements of the following colors: the device red, green, blue and white colors. The luminance measurements Y and the chrominance measurements (x,y) may be taken for a predetermined set of RGB values specified by the following n=4 combinations. Additionally, the (Yxy)j,k values may represent the measurement for the color model k at temperature Tk, k=1 through m and for the combination j, where j may be a natural number from 1 through n=10.
In another embodiment, a color model may be constructed using a look-up table model. The luminance measurements Y and the chrominance measurements (x,y) may be taken for a predetermined set of RGB values specified by the following n=6×6×6 combinations. Six intermediate values may be set for each R, G, B component, and the (Yxy)j,k may represent the measurement for the color model k at temperature Tk, k=1 through m and for the combination j, where j may be a natural number from 1 through n=216.
Moreover, the color models may be a function of multiple input parameters, as opposed to a function of temperature alone. The RGB values, luminance values and chrominance values may be recorded for multiple input parameters. For example RGB values may be recorded for combinations of input parameters such as brightness and temperature. Further, the RGB values, luminance values and chrominance values may be recorded at multiple temperatures at a first brightness level, a second brightness level and so on. Similar to previously discussed methods, the RGB values may be used to determine adjustment values such as attenuation factors. Additionally, interpolation may be used to determine adjustment values for any combination of input parameters and by employing the previously recorded RGB values, luminance values, chrominance values for the various combinations of input parameters.
Insofar as the aforementioned RGB table includes a finite number of entries, during operation of the embodiment the display's operating temperature may fall between temperatures for which entries exist in the table. Certain embodiments may use the existing entries of the RGB table to interpolate adjustment values for such interim temperatures. The adjustment constants corresponding to the interim temperature may be interpolated based on the adjustment constants of the entries in the table bounding the interim temperature (e.g., the adjustment constants for the nearest temperature above the current operating temperature and the nearest temperature below the current operating temperature). Certain embodiments use linear interpolation to calculate the interim temperature's adjustment constant, while others may use a different form of interpolation. Any known form of interpolation may be employed by various embodiments. Accordingly, RGB values may be determined for display temperatures that are not included in the existing RGB table. Moreover, it may be possible to increase the granularity of the temperatures and corresponding RGB values by interpolating between the existing RGB values and determining additional RGB values for temperatures not originally included in the RGB table. In another embodiment, previous adjustment constants may be used to determine a trend and/or a slope of change in adjustment constants to more accurately interpolate the next value.
Although the RGB values, luminance measurements and chrominance measurements have been discussed herein as a function of temperature, alternative embodiments may adjust the color output of a display based on other parameters. For example, the RGB values, luminance and chrominance may be sampled as a function of other parameters including, but not limited to, time, brightness settings, the age of the display or any combination thereof. Accordingly, the RGB table and adjustment constants generated or employed by an embodiment would account for such parameters.
(RGB value)×(adjustment value (RGB)AV)=(RGB)prime
In the operation of block 620, a color model may be constructed. The color model may be constructed as a matrix model or a table based model. As previously discussed, the matrix model and the table based model may yield the same color model corresponding to a specific temperature. In the operation of block 630, a target may be set that corresponds to a specific white point and luminance value. In another embodiment, the target does not have to be a fixed value corresponding to a color. The target may also be a function, and thus be a set of numbers. In the operation of block 640, the adjustment values may be computed and organized into an RGB table of adjustment values corresponding to temperatures. As previously discussed, the adjustment values may be attenuation factors for the RGB channels. In the operation of block 650, additional adjustment values may be determined by interpolating from the temperatures and adjustment values in the RGB table. By employing interpolation to determine these additional adjustment values, it may be possible to determine adjustment values for any temperature. The additional adjustment values may be stored in the RGB table.
The sample electronic display device 801 includes a video-rendering chip 803, a display driver 810, a temperature sensor 807, a heat sink 809, and a display 808. Alternate embodiments may omit one or more of these elements, may add additional elements or may omit certain elements while adding others. Further, it should be understood that the electronic display device 801 is simplified for purposes of this discussion and operating elements not related to the color correction discussed hereafter may be omitted from the figure.
The display device 801 receives video input for the electronic display device 801. For example, a computing device may transmit image information to the device, including RGB (or other color space) values for various pixels or portions of the display 808. The display input includes a plurality of channels, each of which may accept a display input value for a different color.
Video-rendering chip 803 receives the display input. The video-rendering chip 803 performs gain correction on the display input, based on a display temperature, to produce output values. The video-rendering chip 803 then provides the output values to the display driver 810. The display driver 810 controls the hardware of the display 808 to display the output values on the display 808, in a manner known to those skilled in the art and thus not elaborated upon herein.
The video-rendering chip 803 receives the display temperature from the temperature sensor 807. The temperature sensor 807 may determine display temperature by sampling the temperature of the display 808 and/or the temperature of the heat sink 809 that is coupled to the display 808. Based on the display temperature, the video-rendering chip 803 determines one or more gain correction coefficients. The video-rendering chip 803 may determine a separate correction coefficient for each of the plurality of channels of display input values. Thus, for a device accepting input in the RGB color space, the chip 803 may determine a red correction coefficient, green correction coefficient and blue correction coefficient, each of which may be unique and applied to the input value of the corresponding color. The video-rendering chip 803 applies each of the correction coefficients to each of the corresponding channels of display input values received from video input thereby producing output values that have been corrected for temperature.
The video-rendering chip 803 includes a video-rendering engine 804, a microprocessor 805, and a memory 806. The microprocessor 805 receives the sampled display temperature and determines the appropriate correction coefficients for the temperature, as described above. In particular, the microprocessor 805 may retrieve the coefficients from a memory or may calculate them through the use of an appropriate formula relating temperature to the perceived color shift of a display.
In some embodiments, the microprocessor 805 may determine the correction coefficients by retrieving the correction coefficients that correspond to the sampled display temperature from a lookup table stored in the memory 806. The lookup table stored in the memory 806 may include correction coefficients that correspond to the sampled display temperature. Alternatively, the correction coefficients may be interpolated from correction coefficients that correspond to other display temperatures included in the lookup table. For example, the microprocessor 805 may retrieve correction coefficients and display temperatures included in the lookup table, calculate a slope based on the correction coefficients corresponding to temperatures nearest the sampled display temperature, and interpolate one or more correction coefficients that correspond to the sampled display temperature from the calculated slope.
In other embodiments, the microprocessor 805 may determine the correction coefficients by retrieving a correction coefficient formula stored in the memory 806 and applying the correction coefficient formula to the sampled display temperature to produce the correction coefficients. For example, a graph may have been generated depicting the slope of the variance between the display color of a display value on a display and the target color for the display value over a range of temperatures. The graph may illustrate that at a given temperature T, there is a numerical variance between the display color of a display value on the display and the target color. Based on the numerical variance at the given temperature T, a correction coefficient may be determined that, if applied to the display color, would eliminate the numerical variance between the display color of the display value on the display and the target color. A correction coefficient formula thus may be derived from such a graph and allow the correction coefficient to be determined for any given temperature T. It should be appreciated that the specifics of such a calculation would vary based on the particular hardware of a display and thus the formula is not specifically set forth herein, although it may be readily determined for any given hardware profile.
The video-rendering engine 804 receives the display input, as well as the correction coefficients from the microprocessor 805. The video-rendering engine 804 applies the correction coefficients to the display input to produce the output values and provides the output values to the display driver 810. The video-rendering engine 804 may apply a separate correction coefficient to each display input value received on each of the plurality of channels to produce a set of color-corrected output values.
The video-rendering chip 803 also may sample the display temperature periodically. After the video-rendering chip 803 samples the display temperature at a first time and determines correction coefficients that correspond to the sampled display temperature, it may apply these correction coefficients that to all display input values received until a second temperature sampling time is reached. After the video-rendering chip 803 samples the display temperature at the second time, it may determine and use new correction coefficients corresponding to the second sampled temperature. In this manner, the embodiment may employ a set of gain correction coefficients not only at the instant at which temperature is sampled, but also until the temperature is next sampled.
In some embodiments, the video-rendering chip 803 may sample the display temperature at fixed periods, such as every second. In other embodiments, the video-rendering chip 803 may vary the periods at which it samples the display temperature. For example, the video-rendering chip 803 may use the currently sampled temperature as one variable to determine when to resample the display temperature. Continuing the example, the embodiment may be programmed to slow down the temperature sample rate as the temperature nears a set temperature, such as a steady-state operating temperature. Thus, the further away the sampled temperature from the set temperature, the quicker the next temperature sample of the display occurs. In another example, sampling may occur at a first interval below a threshold temperature at power on and a second interval at or above the threshold near steady-state temperatures. As a specific implementation of this example, the video-rendering chip 803 may resample the display temperature after 5 milliseconds if the sampled display temperature at power on was approximately 20-30 degrees Celsius and may resample display temperature after a second if the sampled display temperature near steady-state temperature, approximately 55-65 degrees Celsius.
Three separate 10-bit RGB input values are received at the multiplier 901. Further, the microcontroller 805 may also receive a display temperature from the temperature sensor 807. (Again, it should be noted that the temperature sensor may detect a temperature of the display's heat sink or an area near the display; these are considered “display temperatures” herein.) The microcontroller 805 may use the display temperature to retrieve gain correction coefficients for each of the 10-bit RGB input values from an RGB table stored in a memory. The RGB table generally includes multiple sets of correction coefficients, each of which correspond to different temperatures.
Although a single multiplier 901 is shown, in practice three separate multipliers are used. Each multiplier corresponds to one channel of the RGB color space, e.g., red, green or blue. Insofar as the operation of each multiplier is essentially identical, the function of the red multiplier 901 will be described and it should be understood that the blue and green multipliers work in the same fashion. Generally, the red multiplier 901 receives a red gain correction coefficient from the microcontroller 805, the blue multiplier receives the blue gain correction coefficient and the green multiplier receives the green correction coefficient.
The red multiplier 901 receives the red correction coefficient for the 10-bit red input value from the microcontroller 805. The red correction coefficient provided by the microcontroller has 12 bits of precision. The red multiplier 901 multiplies the 10-bit red input value by the 12-bit red correction coefficient to produce the 12-bit red output value. Multiplying 10-bit numbers by 12-bit numbers produces a 22-bit output. However, the red multiplier 901 truncates the product of the multiplication to produce the 12-bit red output value. In this example, the red multiplier 901 truncates the product of the multiplication because the dithering component 902 may not support RGB values of more than 12 bits. If the dithering component supports RGB values with the number of bits produced by the multiplier 901 without truncation, the red multiplier 901 may provide the red output value to the dithering component 902 without truncation.
The red multiplier 901 provides the 12-bit red output value to the dithering component 902. The dithering component 902 dithers the 12-bit red output value to produce an eight-bit red output value and provides the eight-bit red output value to a display driver. Dithering reduces the bit length of values without the same reduction in quality caused by truncation. In this example, the dithering component produces an eight-bit output value because the display driver may not support RGB values of more than eight bits. If the display driver supports RGB values having a number of bits greater than or equal to that produced by the red multiplier 901, the dithering component 902 may not be utilized and the red multiplier 901 may provide the red output value directly to the display driver.
In operation 1020, the video-rendering chip 803 determines a gain correction coefficient for the sampled temperature. The video-rendering chip 803 may determine the correction coefficient for the sampled temperature by looking up the correction coefficient that corresponds to the sampled temperature in a lookup table, interpolating the correction coefficient for the sampled temperature utilizing correction coefficients corresponding to other temperatures stored in a lookup table, or by applying a correction coefficient formula to the sampled temperature.
In operation 1030, the video-rendering chip 803 multiplies a display input value for the display by the correction coefficient to determine an output value. The video-rendering chip 803 may multiply the display input value for the display by the correction coefficient utilizing a multiplier. The multiplier may truncate the bit length of the output value.
In operation 1040, the video-rendering chip 803 provides the output value to the display. Prior to providing the output value to the display, the video-rendering chip 803 may dither the output value.
Although the present invention has been described with respect to particular apparatuses, configurations, components, systems and methods of operation, it will be appreciated by those of ordinary skill in the art upon reading this disclosure that certain changes or modifications to the embodiments and/or their operations, as described herein, may be made without departing from the spirit or scope of the invention. Accordingly, the proper scope of the invention is defined by the appended claims. The various embodiments, operations, components and configurations disclosed herein are generally exemplary rather than limiting in scope.
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